Methods and system for fast session establishment between equipment using H.324 and related telecommunications protocols

ABSTRACT

Methods of establishing multimedia telecommunication (a multimedia “call”) between equipment (“terminals”). More particularly, the invention provides methods for reducing the time required to establish calls between terminals that implement the ITU-T H.324 Recommendation and other Standards and Recommendations derived from or related to this such as the 3G-324M recommendation developed and adopted by the Third Generation Partnership Projects (3GPP and 3GPP2). More specifically, it relates to (i) a method and apparatus for concatenating the H.245 messages that are required to pass between the terminals at the start of the call to establish the capabilities of both terminals and agree on the type and format of media and data to be exchanged (ii) a method and apparatus for using non-standard H.245 messages or standard H.245 messages with non-standard fields to accelerate such establishment and (iii) a method and apparatus of informing each terminal of the capabilities of the other and proposing the type and format of media and data to be exchanged by means of any user-defined fields that are inserted in the call signaling protocol that is used for bearer establishment prior to the start of the H.324 stage of the call.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/732,917, filed Dec. 9, 2003, which claims priority to U.S.Provisional No. 60/433,252, filed Dec. 12, 2002, both of which areincorporated by reference herein.

COPYRIGHT NOTICE

A portion of this application contains computer codes, which are ownedby Dilithium Networks Pty Ltd. All rights have been preserved under thecopyright protection, Dilithium Networks Pty Ltd. ©2003.

BACKGROUND OF THE INVENTION

The present invention relates generally to methods of establishingmultimedia telecommunication (a multimedia “call”) between equipment(“terminals”). More particularly, the invention provides methods forreducing the time required to establish calls between terminals thatimplement the ITU-T H.324 Recommendation and other Standards andRecommendations derived from or related to this such as the 3G-324Mrecommendation developed and adopted by the Third Generation PartnershipProjects (3GPP and 3GPP2). Merely by way of example, the invention hasbeen applied to the establishment of multimedia telecommunicationbetween 3G-324M (H.324M based protocol) multimedia handsets on a mobiletelecommunications network, and between 3G-324M multimedia handsets andH.323 based terminals on a packet network using a Multimedia Gateway tomediate between the protocols used at each endpoint, but it would berecognized that the invention may also include other applications.

H.324 is an International Telecommunication Union (ITU) protocolstandard for multimedia communication over general switched networks(GSTN). H.324M is an extension of H.324 for operations over mobilenetworks, and 3G-324M is a recommendation by the third generationpartnership program (3GPP) defining adaptation of H.324M for use within3GPP and also adopted by 3GPP2. We call H.324-like equipment devices andsystems employing protocol based or derived from H.324. H.324-likeequipment can connect to other H.324-like equipment via switchingcenters and to other non-H.324-like equipment through multimediagateways. An example of a non-H.324-like equipment is an H.323equipment. H.323 is an International Telecommunication Union protocolStandard for multimedia communication over non-guaranteed bandwidthpacket networks. An H.323-like equipment is an equipment that employs aprotocol based or derived from the H.323 protocol.

Without any loss of generality, we will use the term “H.324” to indicateH.324-like equipment including H.324M and 3G-324M equipment and “H.323”to indicate H.323-like equipment.

Also without any loss of generality we use the term “equipment” toindicate either a user end equipment such as a handset, or network endequipment such as a switch or gateway. We also use the terms “equipment”and “terminal” interchangeably, and they both indicate the same meaningin the present document.

If a call is made between equipments which are an embodiment of theH.324, H.324M or 3G-324M, the first stage of the call is to establish anend-to-end bearer between the equipments. This stage is called CallSignaling and is outside the scope of H.324, except where modems and theGeneral Switched Telephony Network are used. The second stage of thecall is to establish the H.324 session, to provide a means oftransporting video, audio and data between the equipments in a formatthat is known to, and supported by the equipments. In order to do thisH.324M makes use of two further ITU-T Recommendations.

The first of these Recommendations used is H.223 “Multiplexing protocolfor low bit rate multimedia communication”. H.223 specifies aframe-oriented multiplexing protocol which allows the transfer of anycombination of digital voice, video and data (e.g. command and control)information over a single communication link. The H.223 may have anumber of modes of operation, specified in Annexes A, B and C of theH.223 Recommendation that are intended to provide increased resiliencein the presence of errors. These are also known as Mobile Levels 1, 2and 3. H.223 without the application of any of these Annexes is alsosometimes referred to as operating at Mobile Level 0 (base-line). H.324has the concept of Logical Channels which is a way of providing virtualchannels over the circuit switched link. The role of the multiplexer isto combine (multiplex) parts of the data chunks written on the logicalchannels into frames known as a Multiplexer Protocol Data Unit(MUX-PDU). Logical Channel 0 is always available and is used for Commandand Control. Data (voice, video, command and control and other generaldata) is passed to/from the H.223 multiplexer through bitstream chunkscalled service data units (SDUs). Before being multiplexed, thesedifferent SDUs go through Adaptation Layers where extra information maybe added for purposes such as error detection, sequence numbering andretransmission requests.

The second of these Recommendations is H.245 “Control protocol formultimedia communication” which specifies the syntax and semantics ofterminal information messages as well as procedures to use them forin-band negotiation at the start of or during communication. Themessages cover receiving and transmitting capabilities and preferences,logical channel signaling and control and indication. The messages thatare specified in H.245 are expressed in the ITU-T Abstract SyntaxNotation (ASN.1) and can be classified as of Request, Response, Commandor Indication type. H.245 messages are encoded according to the ASN.1standard before being transmitted. When a terminal sends an H.245message of type Request it requires that an appropriate message of typeResponse is sent by the remote terminal. If the Response (sometimesreferred to as an Ack for Acknowledgement) is not received within acertain time, the sending terminal will re-transmit the Request or takeanother appropriate action if no response has been received for repeatedRequests. Re-transmission of requests may occur a number of times. Manyof the H.245 messages associated with call setup are of the Requesttype.

H.245 also requires a reliable link layer for proper operation. Theprincipal means of providing this, specified in Annex A of H.324, is touse the Simple Retransmission Protocol (SRP) or the Numbered SimpleRetransmission Protocol (NSRP), in which one or more H.245 messages,known collectively as a MultimediaSystemControl PDU and in the presentdocument as an H.245 PDU, are formed into SRP Command Frames prior tosending, and the receiving terminal must send an SRP Response Frame(Sometimes referred to as an SRP Ack) to acknowledge correct receipt ofan SRP Command Frame. No further H.245 messages may be sent by aterminal until the SRP Ack for the last message has been received.

The combined effect of the requirement to send an H.245 Response messagefor each H.245 Request Message received, and of the need to receive anSRP Ack for every SRP Command Frame sent means that a single H.245Request message may take some time to be conveyed successfully. Thecommunication involved in sending an H.245 Request message from oneterminal (A) to another (B), and getting an H.245 Response (Ack) messageback is shown in FIG. 1A, which also shows the SRP Command Frames (SRPCF) and SRP Response Frames (SRP RF or SRP Ack) involved when singleH.245 messages are formed into single SRP Command Frames. The H.324standard allows for multiple H.245 messages to be concatenated into asingle SRP Command Frame; however this capability is often notimplemented, in which case such terminals may respond only to the firstH.245 message encountered in an SRP Command Frame. In some cases,terminals which do not support this capability may malfunction uponreceipt of an SDU containing multiple H.245 requests or responses.

We will refer to the sequence of H.245 Request and Response shown inFIG. 1A as a “round trip” and the time associated with completing it asa “round trip delay”.

The key steps involved in setting up and connecting a typical H.324 callare as follows:

-   -   1. Call signaling (bearer establishment)—outside the scope of        H.324. Normally a modem connection if GSTN, through ISDN, or        signaling through mobile switching centers in the mobile case.    -   2. Mobile level detection (MLD)—Where a common Mobile Level is        agreed on between equipments. This step is performed by H.324        equipment that supports mobile extensions such as H.324M and        3G-324M equipment.    -   3. Terminal Capability Exchange (TCS)—H.245 Messaging    -   4. Master Slave determination (MSD)—H.245 Messaging    -   5. Open/Close Logical Channels (OLC)—H.245 Messaging    -   6. Multiplexer Table Entries Exchange (MTE)—H.245 Messaging

Steps (3) to (6) are performed using a sequence of H.245 Request andResponse messages as described above and illustrated in FIG. 1A. Thefull sequence of Request and Response messages involved in an H.324 callis shown in FIG. 1B. Note the order of steps (5) and (6) above can beinterchanged. It should be noted that Steps (3) to (6) relate toprocedures that are defined by underlying state machines that are alsoknown as Signaling Entities. The relevant signaling entities are:

-   -   1. Capability Exchange Signaling Entity (CESE)    -   2. Master Slave Determination Signaling Entity (MSDSE)    -   3. Logical Channel Signaling Entity (LCSE)    -   4. Multiplex Table Signaling Entity (MTSE)

Once these steps have completed, media (video, audio and data) can flowbetween the terminals. Note the H.245 messages flow on the LogicalChannel 0 which as previously described is predefined and carried by themeans of the multiplexer predefined Multiplex Table Entry 0. Once otherMultiplex Table Entries have been exchanged these can also be used inconjunction with H.245 messages.

The key steps above are often handled sequentially; however this resultsin as many as ten H.245 message round trip delays in order to establishan H.324 session with two logical channels in each direction. Inaddition, the SRP scheme (or Numbered version—NSRP, in cases where themobile level is greater than zero) used for H.324/H.245, which requiresan SRP message to be received by the endpoint for every message sent,prior to sending any other message, regardless of whether it isassociated with the same Signaling Entity or not, further limits thescope to pipeline messages on the network, making call setup slower thanif this were not the case. SRP messages are not shown in FIG. 1B.

For H.324M, the Terminal Capabilities Set request (TCS) step describedabove and shown in FIG. 1B is preceded by a mobile leveldetection/multiplexer synchronization phase. This consists of eachterminal transmitting a repeating pattern of bits (flags) that indicatethe highest Mobile Level that it operates at. Each terminal examines theflags that it is receiving. If these flags represent a lower MobileLevel then the terminal drops down to the same lower level. When bothterminals are transmitting the same flag sequence this step completes.

Arising from the set of procedures described above that are required totake place to establish an H.324M call, when a call is made from aterminal which is an embodiment of the H.324 it is prone to suffer fromlong call setup time, which is the interval between the time that thecall signaling is initiated to the time that the exchange of voice andvideo commences between an H324-like end-point (H.324, H.324M or3G-324M) and other terminals whether H.324-like or not.

The ITU Recommendation H.323 uses H.245 in a similar manner to H.324 forsignaling command, control and indication messages related to a call.Unlike H.324, H.323 is equipped with a number of features to speed upthe call setup time between H.323 equipment. Similar techniques existfor the IETF Session Initiation Protocol (SIP) protocol.

Thus there exists a need for techniques to speed up the call setupbetween H.324 like terminals and other terminals either of the H.324type directly, or terminals such as H.323 via multimedia gateways. Thedifferences between the H.324 protocol (and its extensions such asH.324M and 3G-324M) and H.323 and other protocols mean that additionalaspects need to be considered when introducing call establishmentspeed-up techniques for H.324-like terminals. Such differences includethe information about mobile levels where they are used and themessaging and information related to the H.223 multiplexer such as itsmultiplex table entries, adaptation layers and so on.

BRIEF SUMMARY OF THE INVENTION

According to the present invention, techniques for telecommunicationsare provided. More particularly, the invention provides methods forreducing the time required to establish calls between terminals thatimplement the ITU-T H.324 Recommendation and other Standards andRecommendations derived from or related to this such as the 3G-324Mrecommendation developed and adopted by the Third Generation PartnershipProjects (3GPP and 3GPP2). More specifically, it relates to (i) a methodand apparatus for concatenating the H.245 messages that are required topass between the terminals at the start of the call to establish thecapabilities of both terminals and agree on the type and format of mediaand data to be exchanged (ii) a method and apparatus for usingnon-standard H.245 messages, or standard H.245 messages withnon-standard fields to accelerate such establishment and (iii) a methodand apparatus for informing each terminal of the capabilities of theother and proposing the type and format of media and data to beexchanged by means of any user-defined fields that are available in thecall signaling protocol that is used for bearer establishment prior tothe start of the H.324 stage of the call.

These methods may be used separately or severally to reduce the timethat is taken from the point when a user requests the establishment of acall to the point where media starts to be exchanged between theterminals. Merely by way of example, the invention has been applied tothe establishment of multimedia telecommunication between 3G-324M(H.324M based protocol) multimedia handsets on a mobiletelecommunications network, and between 3G-324M multimedia handsets andH.323 based terminals on a packet network using a Multimedia Gateway tomediate between the protocols used at each endpoint, but it would berecognized that the invention may also include other applications.

According to the present invention, techniques for reducing the numberof sequential steps that are required to establish an H.324-like callare provided through a number of methods that may be used separately orseverally.

At least three types of methods are described to reduce the number ofsteps. We call these methods Type I, II, and III, and we number them forease of reference in the present document. Such methods may be combinedor used with conventional techniques depending upon the embodiment. Oneof ordinary skill in the art would recognize many variations,alternatives, and modifications.

In a specific embodiment, the methods are as follows:

-   -   1. Type I: Concatenation of H.245 messages so the number of        standard SRP/NSRP command messages is reduced, in order to start        media communication.    -   2. Type II: Incorporation of H.245 Non-Standard messaging        capabilities to incorporate information about the equipment        involved in the call so the number of H.245 and SRP/NSRP message        exchanges are minimized, in order to start media communication.    -   3. Type III: Incorporation of equipment preferences information        in the call signaling protocol exchange as to eliminate the need        for further information exchange between the equipment in order        to start media communication following call signaling.

In each case the method provides a means to revert to the behavior of aterminal conforming with the H.324 standard.

Type I: Speed-Up by Concatenation of H.245 Messages in SRP/NSRP CommandFrames

This method exploits the capability to concatenate multiple H.245messages within a single SRP/NSRP (H.245 PDU) Command Frame as a mean toreduce the number of H.245, SRP/NSRP messages and associated round-tripdelays. The H.245 messages have to be concatenated in a way as not toviolate dependencies.

The usage of H.245 within H.324 allows equipment to concatenate multipleH.245 elements into a single PDU, thus avoiding the need to use tworound trips for each request/response pair due to the need for anSRP/NSRP response to be received for each H.245 PDU before the next PDUis allowed be transmitted.

The method uses concatenated H.245 to send multiple H.245 messages, eachoriginating from different Signaling Entities that have no dependencieson each other, within a single H.245 PDU.

Interoperability with equipment that do not support concatenated H.245is achieved by noting that such equipment ignore the second andsubsequent H.245 elements in a PDU, so will not send any required H.245Response messages if the ignored message is an H.245 Request message.Therefore the first concatenated H.245 PDU sent should contain at leasttwo Request messages, where the first message must be a Request. If onlythe Ack for the first message is received, the sending equipment willretransmit those Requests and any other messages that have not beenacknowledged, and in doing this and in sending any and all subsequentH.245 messages should revert to sending only a single H.245 message ineach subsequent H.245 PDU. If responses to all H.245 messages in thefirst H.245 PDU are received, the sending equipment can continue to useconcatenated messages. The use of this technique will reduce the numberof round trip delays if concatenated messages are supported. This methoddoes not define any protocol elements additional to those alreadyallowed and defined by the H.245 and H.324 standards. It can beconsidered to be utilizing the existing protocols in a smart fashion,rather than an extension to it.

Preferably, the present invention provides a method of initiating a callbetween users with reduced call set-up times using one or moretelecommunication networks. The method is provided between at least apair of H.324-like terminals coupled to the one or moretelecommunication networks. The method includes transmitting a callsignaling message from a first terminal to a second terminal through atelecommunication network to initiate a call, establishing a bearerchannel between the first terminal and the second terminal once the callsignaling message has been received by the second terminal, anddetermining a common mobile level. Additionally, the method includesdetermining two or more H.245 messages associated with set up parametersfor an initial predetermined mode of operation, concatenating the two ormore H.245 messages into one SRP command frame according to apredetermined size of the SRP command frame, and transmitting the SRPcommand frame including the two or more H.245 messages from the firstterminal to the second terminal through a telecommunication network.Moreover, the method includes transmitting an SRP acknowledge message bythe second terminal once the SRP command frame has been received by thesecond terminal, processing at least the two or more H.245 messagesduring a predetermined time period, and establishing the initialpredetermined mode of operation between the first terminal and thesecond terminal through the bearer channel.

According to another embodiment, the present invention provides acomputer-readable medium including instructions for initiating a callbetween users with reduced call set-up times using one or moretelecommunication networks. The computer-readable medium is providedbetween at least a pair of H.324-like terminals coupled to the one ormore telecommunication networks. The computer-readable medium includesone or more instructions for transmitting a call signaling message froma first terminal to a second terminal through a telecommunicationnetwork to initiate a call, one or more instructions for establishing abearer channel between the first terminal and the second terminal oncethe call signaling message has been received by the second terminal, andone or more instructions for determining a common mobile level.Additionally, the computer-readable medium includes one or moreinstructions for determining two or more H.245 messages associated withset up parameters for an initial predetermined mode of operation, one ormore instructions for concatenating the two or more H.245 messages intoone SRP command frame according to a predetermined size of the SRPcommand frame, and one or more instructions for transmitting the SRPcommand frame including the two or more H.245 messages from the firstterminal to the second terminal through a telecommunication network.Moreover, the computer-readable medium includes one or more instructionsfor transmitting an SRP acknowledge message by the second terminal oncethe SRP command frame has been received by the second terminal, one ormore instructions for processing at least the two or more H.245 messagesduring a predetermined time period, and one or more instructions forestablishing the initial predetermined mode of operation between thefirst terminal and the second terminal through the bearer channel.

Type II: Speed-Up Using H.245 Non-Standard Messages

A second method that is the subject of the present invention forreducing the number of sequential steps that are required to establishan H.324-like call proposes the use of Non-Standard messagingcapabilities of the H.245 protocol. H.245 allows a number of ways ofadding non-standard extensions. There are a number of ways to addnon-standard messages in H.245 in order to speed up the call. The mostinteresting of these is the use of a nonstandard Capability within theH.245 TerminalCapabilitySet message and a NonStandardMessage H.245Response message. These messages can be used to signal that the callingequipment is capable of operating in a particular way, and to provideproposals and preferences to the remote terminal relating to MasterSlave Determination, Logical Channel(s) to be opened and MultiplexerTable Entries embedded within these non-standard extensions toaccelerate call set-up. If the remote terminal supports this method, itwill signal the calling terminal using a non-standard extension whichwill also indicate that it accepts, and may also propose modificationsor provide other information, including for example the MultiplexerTable Entries that it is using.

If the called terminal does not support this method, it will simplyignore the non-standard extension and not respond with the non-standardresponse, but a standard response. The call will then proceed as for astandard H.324-like call. The Type II method does not requirenon-supporting terminals to handle Type I method.

Preferably, the invention provides a method of initiating a call betweenusers with reduced call set-up times using one or more telecommunicationnetworks. The method includes transmitting a call signaling message froma first terminal to a second terminal through a telecommunicationnetwork to initiate a call and establishing a bearer channel between thefirst terminal and the second terminal once the call signaling messagehas been received by the second terminal. The method also includesdetermining a common mobile level for operation. The method provides oneor more custom Non-Standard H.245 messages or custom Non-Standard fieldsin standard messages. The one or more custom H.245 messages or customNon-Standard fields are associated with one or more set up parametersfor an initial predetermined mode of operation. Additionally, the methodincludes transmitting the one or more custom Non-Standard H.245 messagesor custom Non-Standard fields in standard messages from the firstterminal to the second terminal, transmitting a custom Non-Standardresponse message associated with the one or more custom Non-StandardH.245 messages or custom Non-Standard fields from the second terminal tothe first terminal, and processing the one or more custom H.245 messagesor custom Non-Standard fields during a predetermined time period.Moreover, the method includes establishing the initial predeterminedmode of operation between the first terminal and the second terminalthrough the bearer channel based upon at least one or more of the customH.245 messages or custom Non-Standard fields.

According to another embodiment, the present invention provides acomputer-readable medium including instructions for initiating a callbetween users with reduced call set-up times using one or moretelecommunication networks. The computer-readable medium is providedbetween at least a pair of H.324-like terminals coupled to the one ormore telecommunication networks. The computer-readable medium includesone or more instructions for transmitting a call signaling message froma first terminal to a second terminal through a telecommunicationnetwork to initiate a call, one or more instructions for establishing abearer channel between the first terminal and the second terminal oncethe call signaling message has been received by the second terminal, andone or more instructions for determining a common mobile level foroperation. Additionally, the computer-readable medium includes one ormore instructions for providing one or more custom Non-Standard H.245messages or custom Non-Standard fields in standard messages. The one ormore custom H.245 messages or custom Non-Standard fields are associatedwith one or more set up parameters for an initial predetermined mode ofoperation. Moreover, the computer-readable medium includes one or moreinstructions for transmitting the one or more custom Non-Standard H.245messages or custom Non-Standard fields in standard messages from thefirst terminal to the second terminal, one or more instructions fortransmitting a custom Non-Standard response message associated with theone or more custom Non-Standard H.245 messages or custom Non-Standardfields from the second terminal to the first terminal, and one or moreinstructions for processing the one or more custom H.245 messages orcustom Non-Standard fields during a predetermined time period. Also, thecomputer-readable medium includes one or more instructions forestablishing the initial predetermined mode of operation between thefirst terminal and the second terminal through the bearer channel basedupon at least one or more of the custom H.245 messages or customNon-Standard fields.

Type III: Speed-Up by Incorporation of Equipment Preferences in CallSignaling Phase

A third method for reducing call set up times for H.324 terminalsproposes passing information during the call signaling phase (bearerestablishment) where it is possible to embed user-defined informationinto the bearer establishment protocol. This method allows an H.324-likecalling equipment to specify equipment preferences in terms of mediacommunication and the underlying configurations for the multiplexer andthe logical channels. There are a number of ways to represent suchpreferences including preference codes (numeric or alpha-numeric stringrepresenting pre-defined preference configuration) and explicitpreferences expressed in a format such as the ITU-T Abstract SyntaxNotation (ASN.1) format. We call these preferences (coded or explicit)profiles. In the case of explicit preferences or profile, a list ofprofiles can be transmitted as part of the bearer setup signal ormessage. A profile (coded or explicit) specifies exact values for theall aspects of the multiplexer and H.245 channels necessary to set up acall. For example, the Mobile Level, Master Slave Determination, mediaformats for each logical channel and the multiplexer table entries foreach logical channel must be defined. The answering equipment thenselects the profiles to use in user-defined information embedded in thebearer establishment (call signaling) signal or message. This allows theterminals to exchange the parameters of the H.245 channel at the timethe called equipment accepts the call, rather than requiring multipleround trips after the call is accepted.

The bearer establishment (call signaling) is typically specific to thenetwork where the H.324-like equipment is being used. In the context of3G-324M, the call signaling uses an ITU-T Q.931-like call signalingprotocol that allows the incorporation of the preference informationmessages. The Q.931 allows for the incorporation of user-definedinformation in the protocol messages. Q.931 signaling can be complex,but for the purpose of our description here it can be simplified to twomessages. A “Setup” Q.931 message containing the calling partyinformation and other parameter is transmitted from the callingequipment to the called terminal. The called terminal will respond witha “Connect” message to answer the call (e.g. user pressed the answerbutton). In this context the H.324-like equipment preferences areincorporated in the “Setup” message transmitted by the callingequipment. As mentioned earlier the preference messages can beincorporated in the user defined part of the Q.931 message. When thecalled terminal answers the call by transmitting the “Connect” Q.931message, it incorporates its preferred mode of operation in the userdefined field of its “Connect” response message. The Setup and Connectmessages are described further in the ITU-T Q.931 Recommendation and inthe 3GPP technical specification documents. Note that the 3GPP2equivalent documents exist for the CDMA counterpart of the WCDMA 3GPP.

In the case of ISDN networks (e.g. H.324 over ISDN) and networkssignaled using SS7 protocols, a configuration similar to that describedabove for 3GPP can be used.

In the case of GSTN networks, the call signaling protocols such as V.8,and V.8bis can be augmented to incorporate III preference codes.

Ability to utilize coded or explicit preferences overcome somelimitations that call signaling protocols may have on the amount ofuser-defined information that can be included in their messages orsignals.

Preferably, the present invention provides a method of initiating a callbetween users with reduced call set-up times using one or moretelecommunication networks. The method includes providing one or morepreferences for a call associated with a first terminal (e.g., handset,gateway, and other equipment) and a second terminal (e.g., handset,gateway, and other equipment). The one or more preferences areassociated with an initial mode of operation for the call between thefirst terminal and the second terminal. The method also includesprocessing the one or more preferences as a Custom Message (e.g., userdefined based upon preferences) and embedding the Custom Message in apredetermined field of a call initiation message. The method transfersthe Custom Message from the first terminal to the second terminalthrough a telecommunication network using call signaling and processesthe Custom Message by the second terminal. The method includestransferring a Custom Response Message by the second terminal using acall signaling response message to indicate to the first terminal theinitial mode of operation and exchanging information between the firstterminal and the second terminal after the initial mode of operation hasbeen established.

Note that this method of incorporating equipment preference modes ofoperation in the call signaling is particularly efficacious when used inconjunction with H.323 fast connect in the context of an H.324/H.323gateway that mediates calls between H.324-like and H.323-like equipment,respectively. It is similarly efficacious when used in the context of anH.324/SIP gateway that mediates calls between H.324-like and SIPequipment.

According to another embodiment, the present invention provides acomputer-readable medium including instructions for initiating a callbetween users with reduced call set-up times using one or moretelecommunication networks. The computer-readable medium is providedbetween at least a pair of H.324-like terminals coupled to the one ormore telecommunication networks. The computer-readable medium includesone or more instructions for providing one or more preferences for acall associated with a first terminal and a second terminal. The one ormore preferences are associated with an initial mode of operation forthe call between the first terminal and the second terminal.Additionally, the computer-readable medium includes one or moreinstructions for processing the one or more preferences as a CustomMessage, one or more instructions for embedding the Custom Message in apredetermined field of a call initiation message, and one or moreinstructions for transferring the Custom Message from the first terminalto the second terminal through a telecommunication network using callsignaling. Moreover, the computer-readable medium includes one or moreinstructions for processing the Custom Message by the second terminal,one or more instructions for transferring a Custom Response Message bythe second terminal using a call signaling response message to indicateto the first terminal the initial mode of operation, and one or moreinstructions for exchanging information between the first terminal andthe second terminal after the initial mode of operation has beenestablished.

The objects, features, and advantages of the present invention, which tothe best of our knowledge are novel, are set forth with particularity inthe appended claims. The present invention, both as to its organizationand manner of operation, together with further objects and advantages,may best be understood by reference to the following description, takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram useful in illustrating the communications that flowbetween two H.324 terminals when an H.245 Request message is sent fromone terminal to the other;

FIG. 1B illustrates session Set-up for a call between H.324-likeequipment. Note in this case unidirectional video channels are used(e.g. video over adaptation layer AL2 of the H.223 multiplexer).

FIG. 2 illustrates an embodiment of the method of using concatenatedH.245 between two H.324 terminals to reduce connection times for H.324calls;

FIG. 3 illustrates an embodiment of the method of using non-standardextensions of H.245 messages to reduce connection times for H.324 calls;

FIG. 4 illustrates an embodiment of the method of using bearer “user”information to reduce connection times for H.324 calls;

FIG. 5 illustrates an embodiment of the method of using bearer “user”information to reduce connection times for calls between an H.324terminal and an H.323 terminal using a gateway;

FIG. 6 illustrates an embodiment of the ASN.1 Syntax description forType II Request;

FIG. 7 illustrates an embodiment of the ASN.1 Syntax description forType II Response;

FIG. 8 illustrates an embodiment of the ASN.1 Syntax description forType III Request;

FIG. 9 illustrates an embodiment of the ASN.1 Syntax description forType III Response;

FIG. 10 illustrates an embodiment of some coded Profiles, and theirdescription, that can be used in Type III Request and Response.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, techniques for telecommunicationsare provided. More particularly, the invention provides methods forreducing the time required to establish calls between terminals thatimplement the ITU-T H.324 Recommendation and other Standards andRecommendations derived from or related to this such as the 3G-324Mrecommendation developed and adopted by the Third Generation PartnershipProjects (3GPP and 3GPP2). More specifically, it relates to (i) a methodand apparatus for concatenating the H.245 messages that are required topass between the terminals at the start of the call to establish thecapabilities of both terminals and agree on the type and format of mediaand data to be exchanged (ii) a method and apparatus for usingnon-standard H.245 messages to accelerate such establishment and (iii) amethod and apparatus of informing each terminal of the capabilities ofthe other and proposing the type and format of media and data to beexchanged by means of any user-defined fields that are inserted in thecall signaling protocol that is used for bearer establishment prior tothe start of the H.324 stage of the call. These methods may be usedseparately or severally to reduce the time that is taken from the pointwhen a user requests the establishment of a call to the point wheremedia starts to be exchanged between the terminals. Merely by way ofexample, the invention has been applied to the establishment ofmultimedia telecommunication between 3G-324M (H.324M based protocol)multimedia handsets on a mobile telecommunications network, and between3G-324M multimedia handsets and H.323 based terminals on a packetnetwork using a Multimedia Gateway to mediate between the protocols usedat each endpoint, but it would be recognized that the invention may alsoinclude other applications.

The methods described above are generic and can be implemented in manydifferent ways by a person skilled with the field. We describe belowexample embodiments to illustrate the methods which can be adaptedeasily to suite specific equipment needs.

Type I Example Embodiment

In a particular embodiment of this method of concatenated H.245 messagesa terminal combines H.245 Request Terminal Capabilities (TCS) andRequest Master Slave Determination (MSD) messages into a single H.245PDU. It also concatenates TCS and MSD Response Messages (Acks), multipleOpen Logical Channel Requests (OLC) and Multiplex Table Entry SendRequest (MES) in a single H.245 PDU. Finally it combines OLC and MESresponses into a third H.245 PDU. The process of setting up an H.324call between two terminals which support this embodiment of theconcatenation method is illustrated in FIG. 2. The result of adoptingthis approach reduces the number of round trips required for call setupfrom around ten to three. This embodiment requires that the MSDSE andCESE state machines can run in parallel, and that the multiple LCSE andMTSE state machines can run in parallel. This embodiment is merely oneexample of the application of the method of concatenated H.245 messagesin the present invention; other concatenations of messages can beconstructed; these may put different constraints on the signaling entitystate machines within the implementation of H.245.

Optionally, the method also includes reverting to a normal operation ifone of the terminals does not support Type I (i.e. concatenated H.245messages). The calling terminal in this case detects that because itwould not have received the H.245 response to the second of theconcatenated H.245 messages. In this case the calling terminal wouldrevert to individual H.245 messages in the SRP command frames andretransmit the H.245 messages individually from the second messageonwards. There can be many other variations, alternatives, andmodifications.

Alternatively, the method can also be applied to the Numbered SimpleRetransmission Protocol (numbered version of SRP which includes asequence number in the SRP command and SRP acknowledgement frames) andother like variations. Of course, there can be other variations,modifications, and alternatives.

Type II Example Embodiment

In a particular embodiment of the method of using custom H.245 messages,a non-standard Capability is used. An H.324-like equipment requires thatthe first H.245 message it sends is a Terminal Capability Set (TCS)message. The calling equipment includes a capability of typeNonStandardParameter in the TCS it sends to the answering equipment.This capability is identified by a NonStandardIdentifier with a uniqueObject Identifier. This capability contains the additional parametersneeded by the called terminal to start the call, including terminalType(needed for MSD in the same manner as it is required for standard H.245operation) and Multiple Table Entry (MTE) Descriptors. FIG. 6 shows anexample of an ASN.1 description containing the syntax for all of thesedata. By including this NonStandard Capability, the calling party isrequired to accept the decision of the called party as to whether thismethod is used, and what channels are selected.

If the called equipment does not support this method the callingequipment receives a conventional TCSAck and normal H.245 negotiation isthen used to continue the call set-up.

If a called terminal receives a TCS containing the NonStandardcapability relating to this method and itself supports the method, itwill perform a master slave determination by comparing the terminalTypevalue in the received NonStandard capability with the value for thelocal terminal. The highest value will be selected as the master. In theevent of equal terminal type values, the calling terminal will beselected as the master.

The called terminal will analyze the received capability table todetermine the OpenLogicalChannel and multiplex table entries for the newconnection. The called terminal will respond with a normal TCSAck if itcannot derive an acceptable channel configuration, or if it is unable toaccept the multiplexEntryDescriptors provided. The remainder of the callset-up will then be via normal H.245 negotiation.

If acceptable channel configurations and multiplex table entries can bederived, the called party will replace the normal TCSAck with an H.245ResponseMessage of the type NonStandardMessage. See FIG. 7 for an ASN.1Syntax description of the encoded data. The NonStandardIdentifier of thenon-standard response message will have the same Object Identifier asthe NonStandard capability which identifies this method.

Note that the called terminal does not include any additional orNonStandard capabilities into the TCS it sends to the calling terminal,even if it supports this method. The calling terminal must wait toreceive either a TCSAck or the NonStandardMessage before proceeding.

The process of setting up an H.324 call between two terminals whichsupport this embodiment of the method of using custom H.245 messages isillustrated in FIG. 3. This embodiment offers one and a half less roundtrip exchanges than the embodiment of the method of Concatenated H.245.

Capability expressed in the TerminalCapabilitySet request message. Thisensures that the called terminal would not malfunction or hang-up as itis required to be able to handle the case of a non-standard Capabilitybeing communicated to it.

The second key aspect is that the encapsulation of the custom message inthe TerminalCapabilitySet request message allows the terminal totransmit the custom message in the first H.245 message after the mobilelevel determination is done, and hence it does not have to wait.

The third aspect is that the TerminalCapabilitySet request containingthe Type II message embedded as a non-standard Capability can betransmitted using the Type I mode (together with one or more H.245messages).

The fourth aspect is that the called terminal responds with an Ackmessage that informs the calling terminal of the preferred modes of thecalled terminal and its selection of one of the preferred modes of thecalling terminal if the calling terminal presented several preferencesin its Type II message.

Type III Example Embodiment

In a particular embodiment of the method of using call signaling “user”information, Q.931 User-User Information Element is used in the SETUPand CONNECT PDUs. This Information Element is filled with an ASN.1encoded structure (See FIG. 8) including terminalType (needed for MSD inthe same manner as it is required for standard H.245 operation) and alist of profiles the calling terminal wishes to offer. By including thisInformation Element, the calling party is required to accept thedecision of the called party as to whether this method is used, and whatprofile is selected.

Each profile dictates the Mobile Level, Multiplex Table Entries, LogicalChannels used and codecs used for each Logical Channel. FIG. 10illustrates some examples of profiles. The profile contains all theinformation required to immediately begin a call and establish mediabetween the terminals without the need to go through further H.245signaling after the bearer is set up.

If the called terminal does not support this method, the callingterminal receives a Q.931 CONNECT PDU without a User-User InformationElement and normal call set-up is then used.

If a called terminal receives a SETUP PDU containing the User-UserInformation Element relating to this method and itself supports themethod, it will perform a master slave determination by comparing theterminalType value in the received Information Element with the valuefor the local terminal. The highest value will be selected as themaster. In the event of equal terminal type values, a technique such asselecting the calling terminal as the master can be used to resolve theconflict.

The called terminal will also select one of the offered profiles. Ifnone of the offered profiles are suitable then no User-User InformationElement should be added to the Q.931 CONNECT PDU, and the call proceedsas normal.

If a profile is suitable then the master slave determination result andthe selected profile is encoded according to the ASN.1 Syntax for theresponse and added to the Q.931 CONNECT PDU as a User-User InformationElement. FIG. 9 illustrates a particular embodiment.

The process of setting up an H.324 call between two terminals whichsupport this embodiment of the method of using call signaling “user”information is illustrated in FIG. 4.

Embodiment in the Context of a H.324/H.323 Gateway:

A further embodiment demonstrating use with a gateway to an H.323terminal using “FastConnect” is illustrated by FIG. 5. These embodimentsoffer a maximum reduction in call set up time. These embodimentseliminate all round trip exchange for H.245 messages and, for the H.324call segment, initial mobile level detection.

Embodiment in the Context of a H.324/SIP Gateway:

The embodiment in this context is similar to that of the H.324/H.323gateway with the exception that the gateway converts the information(Type I, II and/or III) to SIP signaling messages.

Additionally, any terminal may support Type III and another terminal maysupport Type I/II. Both terminals should be able to operate at theircommon support type (i.e. in this case Type II) as if the callingterminal would not receive the Type III response in the call signalingphase. The general mode is that terminals fall back to the highestcommon mode and within that mode to the highest supported version. Ofcourse, there may be variations, alternatives, and modifications.

H.324 SRP Extension

There is also scope to optimize H.324 SRP to support faster call setup,call tear-down and other session messaging (H.245 Messaging), inenvironments where network latency is significant. One of the featuresof H.324/H.245 is the use of SRP, which provides acknowledgement for alldelivered PDUs. This is useful to ensure that all command and controlmessages have been received at the far end terminal, but provides alimit to the throughput of messages on networks with moderate to highlatency (>40 ms round trip time).

SRP only allows for one message to be outstanding at any time to ensureguaranteed delivery and correct message sequencing. This latency can bemitigated to some extent by minimizing the number of messages exchangedduring call setup such as a message containing multiple Multiplex TableEntries, or combining Terminal Capability Set and Master Slavedetermination messages, however it does still adversely impact the cansetup time.

In addition timeouts are such within H.324/H.245 that if a criticalpacket (or its acknowledgement) is lost during call setup (perhaps dueto data loss) the call may fail, and abort if timer values within stackimplementations are not tuned appropriately.

All of these phases are necessary to remain standards compliant, but itmay be the case that in some circumstances SRP may be used in such a wayto allow messages to be sent while an SRP ACK is outstanding.

In many cases the H.324/H.245 procedures are artificially held back dueto the behavior of H.245/SRP. Essentially independent procedures such asthe opening of different logical channels are unnecessarily coupled bythe requirement that only one H.245 SDU may be outstanding at any time.By removing this limitation for independent procedures it is estimatedthat the time to execute H.245 procedures could be reduced by between50-100%.

Some SDUs must be preserved in strict order, for example with allprocedures, or within a single instance of an Open Logical Channelprocedure, however independent OLC requests do not need to be coupled asthey are in the current standard.

In order to allow new SDUs to be transmitted while SRP ACKs areoutstanding a means of identifying SRPs and associating them with therelevant message is required. One approach would be to use Numbered SRPsare required. The alternatives to this scheme are based on a SelectiveACK, or a sliding window scheme, as described below.

In order to minimize implementation complexity and maintain maximumconsistency it is recommended that a sliding window scheme is used. Thiswill allow the H.324/H.245 implementation to send a maximum of n SRPpackets without corresponding ACKs being received. The H.245implementation itself must maintain locking to ensure that only one SDUACK is outstanding from each state machine instance (typically per H.245procedure), otherwise message sequences within each state machine cannotbe guaranteed.

In order to enable this behavior the H.324 entity must be able to signalto the far end that it is capable of handling this scheme. It issuggested that this be included with Terminal Capability Set, as is thecase with NSRP, but a alternative header field would be required tospecify the remote handling of this case. In the case where the fastconnect scheme described above is used this will have no impact on callsetup time, however it will improve speed and reliability for subsequentH.245 control operations.

The previous description of the preferred embodiment is provided toenable any person skilled in the art to make or use the presentinvention. The various modifications to these embodiments will bereadily apparent to those skilled in the art, and the generic principlesdefined herein may be applied to other embodiments without the use ofthe inventive faculty. Thus, the present invention is not intended to belimited to the embodiments shown herein but is to be accorded the widestscope consistent with the principles and novel features disclosedherein. For example, the functionality above may be combined or furtherseparated, depending upon the embodiment. Certain features may also beadded or removed. Additionally, the particular order of the featuresrecited is not specifically required in certain embodiments, althoughmay be important in others. The sequence of processes can be carried outin computer code and/or hardware depending upon the embodiment. Ofcourse, one or ordinary skill in the art would recognize many othervariations, modifications, and alternatives.

Additionally, it is also understood that the examples and embodimentsdescribed herein are for illustrative purposes only and that variousmodifications or changes in light thereof will be suggested to personsskilled in the art and are to be included within the spirit and purviewof this application and scope of the appended claims.

1. A method of initiating a call between users with reduced call set-uptimes using one or more 3G telecommunication networks, the method beingprovided between at least a pair of H.324-like devices coupled to theone or more 3G telecommunication networks, the method comprising:transmitting a call signaling message from a first device to a seconddevice through a telecommunication network to initiate a call;establishing a bearer channel between the first device and the seconddevice once the call signaling message has been received by the seconddevice; determining a mobile level for operation; performing two or moretransmitting processes within a round trip cycle time using the firstdevice, the transmitting process comprising: transmitting a first SRPframe characterized by a first content from the first device to thesecond device through the bearer channel; and transmitting a second SRPframe characterized by a second content from the first device to thesecond device through the bearer channel prior to receiving a firstacknowledgment from the second device in response to the first SRPframe.
 2. The method of claim 1 further comprising performing anadditional transmitting process comprising transmitting a number ofadditional SRP frames from the first device to the second device throughthe bearer channel prior to receiving a second acknowledgement from thesecond device in response to at least one of the second SRP frame or theadditional SRP frames.
 3. The method of claim 2 wherein the number ofadditional SRP frames is a predetermined maximum number.
 4. The methodof claim 2 further comprising: receiving the second acknowledgement fromthe second device; and determining an association between at least oneof the first SRP frame or the second SRP frame.
 5. The method of claim 1further comprising receiving the first acknowledgement from the seconddevice using a sliding window.
 6. The method of claim 5 furthercomprising receiving the first acknowledgement from the second deviceusing a selective ACK scheme.
 7. The method of claim 5 furthercomprising transmitting a third SRP frame characterized by a thirdcontent from the first device to the second device after receiving thefirst acknowledgment.
 8. The method of claim 7 wherein the third frameis an nth frame that is transmitted n−1 frames after the first frame. 9.The method of claim 1 further comprising retransmitting at least one ofthe first SRP frame or the second SRP frame from the first device to thesecond device after not receiving a corresponding SRP acknowledgmentresponse in a predetermined time period.
 10. The method of claim 9wherein the predetermined time period is associated with a standardtimer.
 11. The method of claim 10 wherein the standard timer is a T401timer.
 12. The method of claim 1 further comprising: receiving the firstSRP frame at the second device; and determining a capability associatedwith the first device based on receiving the first SRP frame.
 13. Themethod of claim 12 wherein the capability comprises a TCS capabilityindication.
 14. The method of claim 13 further comprising: receiving thesecond SRP frame at the second device; and determining a capabilityassociated with the first device based on receiving the second SRPframe, wherein the TCS capability indication is segmented across thefirst frame and second frame.
 15. The method of claim 12 whereindetermining a capability comprises determining an alternative header isused in the first SRP frame.
 16. The method of claim 1 furthercomprising repeating a transmission of the first SRP frame from thefirst device to the second device through the bearer channel, therebyimproving reliability against channel errors.
 17. The method of claim 1further comprising: receiving a message from the second device; anddetermining a capability of the second device based in part on thereceived message.
 18. The method of claim 1 wherein the first frame isassociated with a first state machine and the second frame is associatedwith a second state machine different from the first state machine. 19.The method of claim 18 further comprising delaying transmission of anadditional SRP frame until the first acknowledgment is received inresponse to the first frame, wherein the additional SRP frame isassociated with the first state machine but characterized by differentcontent than the first SRP frame.
 20. The method of claim 1 furthercomprising delaying transmission of an additional SRP frame until thefirst acknowledgment is received in response to the first frame,wherein; the first content is a first logical channel message associatedwith a first logical channel number, the second content is a secondlogical channel message associated with a second logical channel number,and the additional SRP frame characterized by a third content associatedwith the first logical channel number, wherein the third content isdifferent from the first content.
 21. The method of claim 1 furthercomprising using numbered SRP frames to identify a plurality of SDUs.